I'm surprised he didn't mention editing. On a computer this is trivial; on paper you need an ink eradicator, correction tape, or correction fluid. And even those are only good for small corrections. If you want to insert a sentence or paragraph somewhere, that's not really possible with paper.
Also, if you want your text to be published online or printed, it needs to be digitized somehow. Which is a good OCR tool for handwriting, especially if it's not very legible? Just feed scans into Gemini perhaps?
Agreed. As someone who frequently rearranges the structure and order of sentences as I go, I don't even know how to attempt writing by hand. It would be a complete mess. I expect that the common refrain would be wait until the second draft to make such rearrangements, but it's often the bones of the story I'm trying to set properly, and if the bones are broken, there's nothing for the meat to dangle upon.
But maybe it's different for me, since I write nonfiction?
I think writing by hand trains you to be more deliberate when writing. You can't easily go back and make changes, so you have to think ahead more before you write.
For paper it also helps even more than digitally to outline the logical structure of a text before you actually write down full sentences.
I suspect it's because Stepenson stopped editing his work a long time ago.
He used to write a ton and edit it down to a normal-sized book, but once he got popular he just decided to (seemingly) publish everything he wrote, without editing.